Replace manual CLI parsing with clap derive

- Add clap dependency with derive feature for structured CLI argument parsing
- Replace env::args() manual matching with clap subcommands (fetch, best, missing, wishlist, trash, details, track)
- Change print_best_car() signature from (&String, &String, &String) to (&str, &str, u8) for idiomatic Rust
- Add TODO.md tracking known tech debt and planned features
- Update CHANGELOG.md with clap migration details and set v0.2.0 release date

Cargo.toml

@@ -16,6 +16,7 @@ reqwest = "0.12.15"
 tokio = { version = "1.44.1", features = ["full"] }
 serde_json = "1.0.140"
 futures = "0.3.31"
+clap = { version = "4", features = ["derive"] }
 
 [dev-dependencies]
 tempfile = "3.10.1"